I am connected to a data source that will randomly fault and when faulted it stops responding to Mango queries via Modbus TCP and during this time Mango will continue to log new data equal to the last response from the Modbus slave. Mango logs the modbus exception in the events.

How can i stop data logging until the modbus slave becomes active again?

What logging type do you have it set to? If you use "When point value changes" then you won't have data recorded in that period, but it would still appear as a flat line in a chart.

You could try to use the event to disable the points on active and enable them on inactive states of the data source event, but I think you'll perhaps have to leave a point enabled so that it continues polling the device, such to bring the communication event back to inactive.